Over the years I've used a little bit of everything. Sharp small rocks, nuts & bolts, chain, etc. I've not tried the CLR thou....your right about the shaking!
My tank had been repainted (w/ a big sag on one side), so I'm not too concerned about the paints thats on it now. We have a local oil field machine shop that has a caustic tank I've used before to clean out studebaker gas tanks, so it's one of the few "easy" access things we have around here.
Mine's setting with a gallon of mineral spirits in it right now....I came down with the stomach flu the other day & wasn't able to take it to town to drop it off. I'll do that next week.